Assistant Commissioner Mark Rowley said: "I would urge anyone with information about these men, their movements in the days and hours before the attack, and the places they frequented to come forward.

"At any one time, MI5 and police are conducting around 500 active investigations, involving 3,000 subjects of interest. Additionally, there are around 20,000 individuals who are former subjects of interest, whose risk remains subject to review by MI5 and its partners.

"The security and intelligence services and police have stopped 18 plots since 2013, including five since the Westminster attack two months ago."

Following the incident in London on Saturday night (June 3), seven people have died, and at least 48 injured have been taken to hospital.